Mapeamento do epítopo do anticorpo C3C5 da molécula de grânulo denso GRA2 de Toxoplasma gondii e participação de dois prováveis epítopos na indução da resposta imune adaptativa em modelo de toxoplasmose experimental murina

Abstract

Toxoplasma gondii is an obligate intracellular protozoan that belongs to the Apicomplexa phylum and causes toxoplasmosis which is especially severe in immunocompromised individuals and who acquired the infection by congenital transmission. Dense granules are organelles involved in this parasite invasion and replication of the parasite inside the cell. Among the proteins secreted by dense granules, jointly called GRAs, the GRA 2 is particularly immunogenic. In the present work, we aim to study the role of this protein in inducing adaptive immune response by produced and characterized a monoclonal antibody against GRA2. The parasite treated with this antibody showed the lowest rate of replication in intracellular proliferation assay compared to treatment with irrelevant antibody. The epitopes of this protein that binds to the monoclonal antibody have been mapped by phage display. Through bioinformatics analysis, epitopes for B cells and T GRA2 were predicted and based on that and on the results of phage display amino acid sequences were chosen to synthesize two peptides that were tested as potential vaccine. Immunization tests were carried out in C57BL/6 mice with synthetic peptides and these animals were subsequently infected with T. gondii. There was a significant reduction in mortality in the group immunized with the mixture of both peptides. The negative control group, immunized only with BSA, showed the highest mortality and analysis of cytokine present in the sera of these animals there was a predominance of proinflammatory cytokines while antiinflammatory cytokines were shown to be almost nonexistent in the serum of these animals. Given these results, it was found that the group with higher survival showed better Th1/Th2 balance. This demonstrates that immunization with epitopes recognized by both B cells and T cells appear to be more effective. Thus, peptide mimetics GRA2 regions of the protein may be likely candidates for the development of vaccines against toxoplasmosis.